Centralized traffic control system for railroads



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N. D. PRESTON El' AL CENTRALIZED TRAFFIC CONTROL 'l'S'ElVl FOR RAILROADS Dec. v14, 1948.

Filed May 14, 1945 Dec. 14, 1948.'I N, D, PRESTON r- T AL v 2,456,533

CENTRALIZED TRAFFIC CONTROL1-SYSTEM FOR RAILROADS s sheets-sheet )2 Filed May 14, 1945 IA.' w-

Bnventons gw' ll ill Dec. 14, 1948. l N. D. PRESTON Er An. 2,455,533

CENTRALIZED TRAFFIC CONTROL SYSTM FOR RAILROADS Filed May 14. 1945 8- Sheets-'Sheet 3 Fa. 2A

Suventor:

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. i943. N, D, PRES'f-QN El' AL v 2,455,533

u CENTRALI'ZED TRAFFIC coxjITRoL SYSTEM FOR RAILROADS i I i l l los f/f I 1Q;

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I n 1' K v lfm :im l l I 121% l [26 nventors Dec. 14, 1948. N. D. PRESTON Er -AL CENTRA-LIZED TRAFFIC CONTROL SYSTEM FOR RAILROADS 8 sheds-sneer `5 Filed May 14. 1945 m .oi

Dec. 14;1948. N. p. PRESTON n AL 2,456,533

GENTRLIZED TRAFFIC CNTROL SYSTEM FOR RAILROADS www Dec. 14, 1948. 2,456,533

CENTRALIZED TRAFFIC CONTROL SYSTEM FOR RAILROADS Filed'uay 14,A 1945 v N. D. PRESTON El AL" 8 Sheets-Sheet 8 lha-Ve Patented Dec. 14, 1948 UNI TED v artistes CENTRALIZED -frimFFIQ-conimoLfsysmEM v1F01?, -RAILRDADS NelD. Preston and ForestB; lter, vN.l Y., -ass'ignors to Ge Company, Rochester, N.

Application. Mayl14, 1945, Sciaa 5,937,157 6l ..1 This invention relates to 'code communication `systems of the carrier frequcncytype,"an'dniore particularly to such a communication systemfor centralized tra flic 'control systems 'on' railroads,

Generallyspeaking, 'a communication system 'is his control, and also the movement of trainsinto and out of approach and detector track sections. Systems of this characterare in use, landtheir functions, characteristic features and mode Vof operation are generally familiarto those skilled in the art.

Code communication systems of this type 'which employ direct current impulses of different polarity, duration or spacing applied to line circuits, been developed and are in practical use,'but in `various applications of centralizedtra'flic con- 'tro'l systems to railway operation, and also for other communication purposes, it 'is fdesirableto have a communication system operating by transmission of carrier frequency impulses for use in connection with a radio or space radiation type of system, or in connection withflin'ecirc'uits utilized for other facilities, such as power 'transvmission, telephone, 'telegraph or the like, `where it is desirable to avoid changing the continuity of the 'line circuit by opening it for communicaf' tion purposes, or changing its electrical characteristics by a shunt, or applying vdirect current impulses to interfere with such other facilities.

The primary object of this invention is'to provide such a communication system which 'will operate over a line circuit, or by space radiati'on, by transmission of carrier frequency pulses, with or without modulation `-by control tones, insuch a manner as to aiord all of the necessari7 Oper'- ating characteristics and features required Iof vsuch a communication' system suitable for centralized trafe control 4systems for railroads, fin'- cluding provisions for exercising a predetermined priority or preference as between any plurality o'f eld stations having new indications to transmit tothe control oiiice at the same time.

A further object of the invention'i's to attain 'these functions and operating characteristics I`in a simple and effective Way with 'conventional relays-and other well known apparatus, and? to 55 ili-ority provide for f rapid and `'reliall'e fc'ode transmission, v`more"partieulaly by using'snort Iperiods for foon- "uitioning enfcleareout at theibeginning' anu fend respectively of each operating cycle, so `to lilo- Ita'in a shorter total time Afor an'l'operating cycle *of aA given 'number ofs'teps', rasfcrfipared Withfthe usual =`practice for employing slew-release fre ys ro obtain conditioning and ciearout period-s' 'uis- '-f active-fromotherintervaisiin transmission Iand =reception y'of""cotle yzeler'iients' i-iiiingtlie operating cycle, Hue to the prolonged duration -of suoli *co-'nditioiiin-g "and clear-'aot 5periods'.

' frlieorganiaation of partsand; :r'ciiiirscoi'fistiA- acting the Lsystem of this' @invention involves tarietyof interrelatedrunctios A, 1 `rcounivdive-ti to summarize rieiiy rc1 "clean "f; but w certain '1reatures'- and functions characterizing Lthe invention mayflbeipoiritedout tela-avantage vio-e"f`ore l-"descrilmingthe 'tem fin 'lietail.y

Generaliyts'p nggttnd" ithoiit attempting' to Henne-'the iiaturefor scope yofthisinvention,itlis proposed to vutilise ca -oistinetivefcharacrerro l `fruttetiats eintervalsentregan: operating vdesiren'controls'and ndications-Storanifitroi the field :istat-ions :as elected one fat'a time curing "difeett 'control "dlindic-atiozi fcyc'les. lorgan-i at of ltliersys'tmof fthiS-Sinvention,two 'different arrierifrequencies,conveniently termed 'anota 'iemproyedlto-g'ive distinctive char- 'facterft the cotlee'lements f'transmitted-fror'n the icontroi cinco 'fto the' :new stations; :and the code Ae'len'i-:nts' transmitted iirorri the :field fstations "Eto iure-z ccntroloiee are distinct-neun character by reason -of *the *transmission "or non-transmission dif-another 'ierffrequencyueat:predeterminati *itf nites in the operating `cycle existing Vbetwee'nl ransinissi'cin pulsesioflthe ca ririerffrequ -y` l from-the'rcofitro12o'mce- :In ja moiei frganization .of "the system, :suitaiie ffnrfeorrfmunication by mation, as weil fas over a urne uitthe control-Dse fmociulates one neri ifreqiiency "with V'different icontrol:tones itt'i verdistinctive-character to ats cone lements, while fthe field stations transmit, -oriiau-to transmit I t ipredetermineuton". interf- :valls in-ftlie voperati cycle', vipul'ses llo'f fthe same cartieirfrrequ'ncywithout anyimodulation.

lnti-11 spealrrinfgf'generallywithlregarufito .tire rea it" .of the :system tof this :inventiongr another `e vact 1ciistnat the cessaryipreerenceor whatweenianiyipiufaiityfor neldstations paratus and gitane ready to send indications to the control oiiice during an indication cycle, is exercised on the basis of the relative superiority of the code call allotted to the various field stations, in accordance with the general principles disclosed in our prior Patent No. 2,129,183, September 6, 1938. In the case of the present carrier frequency system, however, the field station or stations with a superior code call does not exercise its code superiority directly against other stations by controlling a line circuit, as in our prior patent, but such code superiority is exercised indirectly through the agency of code elements retransmitted from the control oice in response to code elements received from the field stations, with the appropriate priority determined by the control office apparatus. Stated more specifically, each field station, having new indications to transmit to the control oiiice during an indication cycle, has anvopportunity during the iirst off interval to send to the control office a code element having its character dependent upon the first code element of the codecall allotted to that station; and during the next succeeding on interval, the control oce transmits to all of the field stations a code element dependent upon that received from these field stations, acting automatically to send one predetermined superior code element in preference to another inferior code element, if this is called for by any one of these field stations. Such repeating transmission of a superior code element from the control office, when called for, will automatically cause each of the field stations, if any, having a corresponding code element of the inferior character in its station code call, to drop out for that operating cycle, leaving only those field stations having a superior code element in their station code calls effective to transmit to the control office during the next off interval.

The same operation of transmitting station identifying code elements from any remaining station to the control office during off intervals, the repeat or retransmission of code elements of a like character from the control office to such remaining station or stations vduring the next succeeding on intervals with the necessary priority, and the dropping out of a station as soon as its code does not reach the code elements transmitted from the control office, may be repeated for as many step intervals as desired, until only one station having the most superior code call of the plurality initially acting remains effective, whereupon this particular indication cycle is carried on with transmission of indications from 4this surviving field station. Other features of this organization for providing the necessary priority between the field stations trying to send in indications to the control oice at the same time will be explained later in discussing the apcircuits and their operation in detail.

A still further characteristic of the system of this invention relates to the restoration of the apparatus in the control office and at the various field stations to the normal at-rest condition at the lend of each operating cycle. In accordancey with this invention, this restoration or clear-out is accomplished quickly by a distinctive transmission condition of both frequencies or control tones from the control oiiice simultaneously. In addition to providing such clear-out control at the end of each operating cycle, provision is made to give this clear-out control automatically whenever a prolonged energization or deenergization of the line circuit occurs during an operating cycle, so as to obtain results comparable with the symbols (-1-) and arranged to be energized from a split battery,

those where the clear-out is obtained by the release of slow-acting relays in response to a prolonged deenergization of the line circuit. In this connection, special means is also provided to avoid improper operation of a field station equipment when it is re-connected to the line circuit, after having been disconnected for some reason, as explained more in detail later.l

Various other characteristic features, functions, attributes, and advantages of the system of this invention will be in part apparent, and also explained as the specified embodiments of the invention illustrated are described.

In describing in detail, the particular embodiments of the invention herein disclosed, reference will be made to the accompanying drawings which illustrate, in a conventional and diagrammatic manner, the various parts and circuits of the apparatus for the control ofi-ice and one typical eld station, these parts and circuits being shown more with the view of simplifying the illustration and facilitating an understanding of the organization and its operation, then for the purpose of showing in detail the structures and circuit connections preferably employed in practice.

Various conventional illustrations and symbols have been employed in these drawings to simplify the representation and understanding of the relays and circuits. The contact iingers of the various relays, which are identified with their respective coils or windings by dash lines, are shown in ahorizontal or raised position when the relay is energized, and in an inclined or lowered position when therelay is deenergized, regardless of the location of the contact ngers with relation to its operating winding. Instead of showing all of the wiring Yconnections to the terminals of a battery, or other suitable source of current, the ends of wires connected to the opposite terminals of such a current source are designated by arrows, pointing toward or away from the wire and indicating the flow of current into and out of the circuit, with Certain circuits are and connections to the extreme terminals are designated for convenience B B, and the connections to the mid-tap by the letter C.

Various relays, such as the relays of the stepping bank, are employed in the control office and at each of the field stations to perform the same function; and for convenience these relays are identified with the same letter, with a prefix l for those associated with the typical field station equipment shown. Various other schematic and diagrammatic representations used in the drawings will be explained as the description progresses.

In the accompanying drawings, Figs. 1A and 1B, when arranged side by side, illustrate the relays and circuits for the control ofice; Figs. 2A and 2B side by side illustrate the relays and circuits for a typical eld station; Fig. 3 comprises explanatory diagrams or graphs to illustrate the periods or intervals of energization of the line circuit, or transmission of carrier frequency by space radiation, during typical control and indication cycles; Figs. 4A to 4H show time or sequence charts or diagrams for certain relay-op erations in the control oice and the typical iield stations involved in various periods or stages of typical control and indication cycles, for the purpose of facilitating an explanation and understanding of the operation of the system; and Figs. 5 and 6 show certain parts of the system involved encaisse in modifications using one carrier :frequencyand two control tones.

GENERAL ORGANIZATION The purpose and general mode vof operation of code communication systems for vcentralized traiiic control systems are explained in` AVarious prior art patents, such as our Patent No. 2,129,183, September 6, 1938; Halles, et al. .No. 2,259,561, October 21, 1941, and Judge, et al. No. 2,082,544, January 1, 1937. In brief, the primary purpose of a code communication system of this character is to provide for the transmission of controls and indications between a control oice l.and ya plurality of iield stations located at various points along the railroad adjacent switches and signals. The particular way in which the controls govern the operation of switches and signals forms no part of the present invention, and one typical form of such control circuits is illustrated vand described in detail in the patent to Wells,` No. 2,159,922, May 23, 1939. The indications received in the control oiiice are usually employed to control the lighting of small indicating lamps associated with a track diagram, control levers and the like, as explained in our prior 4Patent No. 2,129,183 and the others above mentioned.

A typical centralized traine control system ordinarily involves a number of different field stations at spaced points along the railroad; but since the apparatus and circuits for these various field stations is generally identical, except for certain connections or code jumpers for setting up distinctive code calls for the respective stations, and

perhaps in the number of devices to be controlled I or indicated, it will be sufficient to show and explain these apparatus and circuits for one typical eld station, such as shown in Figs. 2A and 2B, with such reference to operations occurring at like neld stations as may be necessary.

The control oiiice in this system may be located at any point with relation to the location of the field stations, so long as it is within effective range. The equipment located in the control oilice comprises certain apparatus and connecting circuits, such as control levers, indication devices, and the like, which relate to individual field stations and are merely duplicate devices having the same function; and for the purposes of understanding the present invention, it is suilicient to illustrate and describe the operation of certain of these devices as typical o'f all the others, with the understanding that there are .in fact a number of such control levers, indication devices and the like in the complete system.

In the main form of the invention illustrated in Figs. 1A, 1B, 2A and 2B, itis contemplated that the communication system of the invention will operate over a conventional two-wire line circuit, to which there are applied various other communication facilities, such as a telephone or telegraph system of various types, including carrier current frequency systems, or a telephone despatching'system with selective ringing, alternatcurrent power transmission, or other facilities requiring that the continuity and electrical characteristics of this line circuit should not be interfered with by the operation of the communication system. Such additional facilities on the same pair of line wires with the communication system of this invention may take various .forms and have not been shown.

The line circuit used with this invention is, of course, provided with appropriate terminating impedances (not shown) .at Vits end or ends- .beyond ithe ield .stati-on .remote from the. :control `niiicann'th rdue .regard :to Athe ilocation of 'the :toontrol cnice. 'and :the characteristic impedance of rthe line circuit, :in accordance with well vknown `lprinciples Land 'spractice )for carrier .current 'transmission on line circuits. Such line circuit termination visrnot :only desirablef-.or effective fenergy transfer totheline circuitpbut may benecessary sin-asystemof this type'to avoid wave `reflection .from "the end or'ends of the line circuit and .for- .mation :of `so-:calleid standing waves lto "create a :nodal point of izero .or low energy level where ya .fieldrstation is tobe located, lwith :the result that suon-field `wouldnot respond to the carzrierfrequency appliedin the vcontrol oflice. When I,the .line :circuit is properly terminated, however, .eachf-Dfithe field stations connected toit .will yre- .'cieive :adequate energyfrom the carrier frequency transmitted from the control oce regardless "of their particular location.

:Since such .additional facilities -on the same .line circuit may impose limitations as to the carrierfrequency available for this communica- .ti'on system, asideffrom the attenuation characteristicsof `:the line circuit, so that the carrier frequency chosen vfor a communication system ofitl'lis'invention'is of an order not well adapted .for tone.,modulation .and efcient filtering, it is .proposed to 'employ two different frequencies fl and #2 forgiving rdistinctive character to the fcode elements `transmitted from the control .oicefand another diiferent yfrequency f3 for pulse 'transmission from the 'field stations, together with, such .connections between the `generating and receiving means for such frequencies and the line circuit .fas will not interfere with the 4adfclitionalfacilities von the same line circuit. While `vario'ns .frequencies .may be employed for this 'pur-pose, it .is preferable to use a frequency f3 4furthe-field station pulses Which is substantially different from both of :the frequenciesI fr and t :transmitted from the control oflice, in order :that the :necessary discrimination later discussed may b'e .obtained by relatively simple and low floss iflters. :The Vfrequencies yl and f2 for control .office transmission `may be more nearly alike, `sinne .the'lters to discriminate `them .are operated at the same energy level. The choice of these .frequencies .largely depends upon the other `facilities on the line circuit; but frequencies ,of v3,000and 3,200 cycles per second for fl and f2, and a 'frequency of 45000 for the .frequency f3, are 'typical examples of suitable frequencies for use "withthe 'facilities ordinarily used on line circuits along railroads, including carrier current telephone or telegraph.

For the purpose of generating these carrier frequencies ina controloiiice and at the various field stations, anysuita'ble frequency generating means `may be employed; but it is considered 'preferable `to use vsome yone of the well known lforms-'of a self-starting'vacuum tube power oscil- .lator having a frequency stabilization within `range of the lter limits. Since oscillators of this -type are well known'in the art, such oscillators designated OSC-Jl, OSC-42 and OSC- f3, as the 'generatingm'eans for the frequencies 'fl andfyZ in the control office and the frequencyf?. at the ld-statiom'have Abeen shown schematically .in block form.

In the particular arrangement shown, these voscillators are .normally inactive, and .are .set .into operation .by connectinga suitable source Aof .voltageBB `to the output plate .circuit of .the oscillator, .which .is coupled to `the line .circuit through a coupling transformer TF connected across the line circuit through the usual coupling condensers. The two oscillators OSC-fl and OSC-fZ for the frequency fl and f2 in the control office in Fig. 1A are controlled through front contacts 5 and 6 of transmit relays PI and P2; and at the field station the oscillator OSCS for frequency f3 is controlled through a front contact `l of a pulsing relay PL and a front contact 8 of a pulsing repeater relay PLP, which is energized by an obvious circuit through a back contact 9 of relay PL. It can be readily seen that, when the pulsing relay PL at the field station in Fig. 2A is energized, the oscillator OSC- f3 for frequency f3 is rendered effective to deliver a pulse of frequency to the line circuit, until the repeater relay PLP releases, the duration of this pulsing being determined by the release time of the relay PLP.

The impulses of carrier frequency appplied to the line circuit energize suitable frequency responsive means in the control office and at each of the field stations. In the case where pulses of the frequency f3 are received from the eld stations, these pulses are supplied through the coupling transformer 'IF in the control oflice to a suitable band-pass filter BP-S for the frequency f3, shown schematically in block form, provided both of the control office impulsng relays PI and P2 are deenergized at the time to close their back contacts I0 and il. The output of this filter BP-JS is connected to a suitable amplifier AMP, and thence to suitable relay means. This relay means in the control oice is preferably adapted to respond to pulses of short duration; and although any device suitable for this purpose, including an electronic means, may be employed, there is shown a polar magneticstick type of sensitive relay M with two windings,

'which operates quickly in response to the energization of its upper winding as a result of a short ypulse of the frequency f3 to move its armature and contact fingers shown conventionally from the normal position shown to the right-hand dotted position, and which acts to hold its contact fingers in this operated position until restored by energization of its lower winding from a local source in a manner later explained.

In connection with this transmission of pulses of the frequency f3 from the field stations, there are conditions later described where two or more field stations may be applying such pulses at substantially the same time during the station selecting and registration part of an indication cycle; and since these eld stations have different oscillators for generating the frequency pulses, there is the possible contingency that a certain phase relation of these pulses of identically the same frequency are applied at the same instant by different field stations to create a condition where such pulses in effect neutralize each other at the control omce and fail to operate the message relay M. Although the oscillators at the different field stations may be constructed and coupled to the line circuit in such a way as to tend to operate at the same frequency, the variable distances between field stationsand the control office encountered in practice, and the phase shift resulting from the line circuit characteristics, does not always assure the energy at the effective operating level will be received at the control oice when certain field stations are applying a pulse of the frequency f3; and it is contemplated in accordance with this invention that no attempt will be made to synchronise the oscillators of the field stations, but rather allow ytheseoscillators to operate at their own individual frequency and in such time phase relation as they happen to start. In this connection, it can be appreciated that the existence of complete phase opposition and neutralization of the energy received at the control oflce from different stations is extremely remote, where there is necessarily slight variations in the frequency generated by these different oscillators and their phase relationship, as well as the time at which these oscillators actually start transmission. Even if such phase cancellation should occur, and the control ofce should fall to receive a pulse created at different eld stations, such field stationsk would drop out, as later explained, and merely an idle or ineffective indication cycle would result; and it is most unlikely that the same phase relation and other conditions causing such phase cancellation would exist on the next or some other subsequent cycle, so that in due time the indications from the stations in question would be properly received..

Since the filter trolling the relay M is disconnected by contacts i3 and ii from the line circuit when either` relay Pi or P2 energized to apply the frequency fl or f2 to the line circuit at the control oice, this filter associated with the relay M does not have to discriminate against the frequency fi or f2 at a high energy level, but merely has such filtering characteristics as are needed to protect the relay M against false operation by the other facilities on the sarne line circuit.

The impulses of frequencies il or f2 or both transmitted from the control office to the field .stations during the operating cycles are employed to energize receiving relays F! and F2 of the neutral type at each field station through band-pass filters BPH and BPZ and power amplifiers AMP in a similar way, as shown in Fig. 2A. In this case, both of the filters are effectively disconnected from the line circuitby a back Contact ld of the pulsing relay PL and a back contact l5 of the pulsing relay PLP, While a pulse of the field frequency f3 is applied by the operation of relays PL and PLP, as can be readily understood.

It may be explained at this point that, although the receiving relays Fl and F2 at each field station are effectively disconnected from the line Vcircuit at that station whenever the field of `frequency f3 is applied, a pulse of the frequency f3 applied to the line circuit at such station at a high energy level suitable to reach the control oiiice will also be transmitted to a nearby station at which the filters and amplifiers for relays Fl and F2 ma-y be still effectively connected to the line circuit. Since the filter and amplifier for each of the receiving relays Fl and F2 must have sufficient sensitivity to respond to frequencies received at a relatively low energy level from the distant control office, it can be seen that the intensity of the pulse of frequency f3 received from a near-by eld station may well be much greater than that for which the relays Fl and F2 are designed to respond. In other words, a field station, particularly one remote from the control oiiice, may have a strong pulse of the frequency f3 applied thereto from a nearby eld station tending to energize improperly the relay Fi or F2; and for these reasons the lters associated with the relays Fi and F2 at the field stations have to be designed to discriminate against pulses of a different frequency f3 at a high energy level, as compared with the frequencies fl and f2 which these filters are designed to pass. Accordingly, as previously noted, it is BP-S and amplifier AMP con' 9a desirable to employ for the field frequency f3? one that is suiiiciently sep'arated'from either of the other frequencies-i f'I and f2 to enable such dis.'-' crimination to be accomplished effectively.-

In th'isv connection, the pulses ofthe field' frequency ft are preferably made. afs-short as prac-- 'ticable and still obtain satisfactory response of the receiving means, such.' the relay M at the distant controloice," andzwitn' suchsliort pulses Lof the iield fr'equency'fS-,the receiving relays FI. :and F2 at the fieldstations. may be" cons-tract''ed to be too slow in their operatiorilto res-pond'to such pulses, particularly atthere'duc'ed energize-y tion permitted bythe associated lters. Also, if desired, the coupling transformer ITF', or some other element involved in the eiiecti'vei operation of the relay FI or F2 vfrom line circuit energy, may be designed. to permit passage of a amount of energy to the'y amplifier, by c'oresaturation or otherwise., so that. substantially the same energy level of. frequency i'sf'ap'pl-ie'ell to the amplifier and relay' irrespective or. the. intensity of the frequency on the"y line circuit. Itsmay' be added that such cross-fire eiect in the energize;-y

tion. .oiareceivingrel'ay FI orlzat one'iileld: station by a pulse 'ofi-the ne'ld frequency s-fat. a near-by station should. be avoided',.be'causer such operation' of the-relayl'ft' or'FZ will tend'to cause premature or' ifm-proper stepping" action.

Inv addition to' the'y equipment justdescribed for applyingl and? receiving'. carrier' frequencies '0n the line circuit, the. control cnice equipment in' Figs. 1A and' 1B include" a lliner'ep'e'ater' relay FP', cycle' marking relayiCY,: aclarar-out' relay CO, a bank or stepping. relays VL-AVLt and? ariiasso-V cia-ted nalfstep. relay VF of the. usuali type', a

manually operable" start button. I PB (rone'ffo'r'ea'ch.

station) and associated repeater stick relay' I PBR, and code determining relay tCDf, a niasterr relay' CDS associated' with tl'ie'f'co'debl determining relays such yas ICDga plurality or controla-.leversrepresented' by* the typical'. eontrol leverfSWIzL, ay relay C for initiating a control cycle; a1 relay'FC energized by aiie'lclstartioi.' initiating alfi'indi.` cation cycle, a group of station registration relaysre'pre'sented" by' they relaysl ISR and 28E; and" a number of indication responsive devices; repre- .sentedLv by the' indication. magstick relay" ITK?, together with other parts and circuits-more Convenie'ntly discussed'. in' describing' the operation'. l

Referring to"l"i\'g"s.V 22S; and 2B; the typical eld' station eq'uiifimen't'V includes aline repeater relayv iFP", a cycle marking relay f'CY, anl'ocko'ut relay IL, a back of stepping :associated relay' WP, stationselectifn'g relays-- ISI :and ISO for in'dication4 andeontroiVcycles1re-- speoti'vely, a plurali-ty ofy con-trol responsive de'- vices represented by the typical" control vmag-- sti'ck'f relay' WZ', and'i afplura'lfity' orf-:devices v to be :indicated inthe' controlI oice represented by the' -traclcr'elays ITR- and ZTltftogetli'er'witli aclia'nge relay' .ICH and a repeater'relay' IICHP' for providing' a field start.

The banks of'stepping relays Vl to and tliev associated? lialf-st`epy relay VP', the" control 'ofliceand' at' each elldi'sta-tion, are' op'eratedby the' intermittent energi'zation ofthe line-repeater re'- lay FP in tiie.- saine'- manner deseriberil'in detail in prior' patents', such asJud'ge; Noi 2,138,863;

December 6", 1938, and Pres'teni'Noi 08224662 June-l 1 1937; and. it will b'e s'uil'lci'en-t'- for' an understand-ingn of' the present invention to'p'olnt" out briefly the conditionsiunder which thesestepping relays Vie-V12'. and tlie nalfbstep relay-"VP are operated? with respect to the: energieaiiion andv limited;`

d'eenergization of the line circuit during the' on and oli intervals, Without tracing in detail the various circuits involved,

Considering brieiiy the operation of the step'- by'st`ep devices in the form of the stepping relay bank and and 1nali-step relay VP as shown in the control oiiice in Figs. 1A and 1B, all of these relays are dee'nergized asv shown rest condition of the system. energizatio'n of the line circuit from the control oilice during the conditioning period, the relay VP is energized. by a circuit readily traced through front contacts I6 and I 'I of relays FP and CY, andback contacts of the steppng relays, and is maintained energized by a stck circuit through its front contact i8 to prepare a circuit by which the rst step relay VI is energizedl during the rst o interval or deenergization of the line circuit at the control oilice. The release ofthe relay FP in this ofi interval, with the relay VP" energized, causes energization ofA the first step relay VIl through a front contact I9 of relay CY and a back contact 2G of relay FP; andthe step relay VI is held up by a stick circuitthrough front contact the' end of' the cycle.

During the rst During the next' on pefrequency fI or f2 from the control oillce, the resultant energization ofthe relay FP causes thel relay VP to drop an'd prepare an energizing circuit for 'the next step' relay V2'. The sameA operation isv repeated for any desired number of steps.

Thus', as indicated in the diagram of Fig. 3`, the half-step relay VP is' picked up andreleased during the alternate on intervals, While the step relays VI, V2, etc'. are successively energized during the 01T intervals,

The control of'ce also includes a relay E intermittently energized by the operation' of the stepping relays VI-VI and the half-step relay" VP in a manner' described, for example, in thev patent to Hailes etal., No. 2,090,912, August 2&1', 1937; Briefly stated, and as indicated in'diagram of Figi 3, the relay E is energized each time the half-step relay VP shifts, i. e., becomes energized or deenergize'd, and the relay Ereleased when the next step relay VI, V2, etc., is'energized. In short, the' relay El goes up and dovvn'y alternately in response tothe operation ofthe' stepping relays' in the control oiiice, and servesv to control the operation of the transmit relays P'II and P2, as later explained, toforml the on and ofi intervals of energize,- tion and deenergization of the line circuit from' the control oice.

TYPICAL. OPERATIONSFOR THE SYSTEM Under thenorma'l at-re'st condition, when. the

system is not operating to transmit" controleren" indications, the line 4circuit is deenergized, and' most of the relays in the controlofljc'e and 'alti the.`

control oiic'e from a'iield stationby an. .automatici eld start pulse transmitted from such field' sta'- tion. upon a' change in the position or condition of some device, such asa track relay, at that 'fieldstation requiring transmission of a new indication tothe control oi'ce.

The' system is' simplex2 in its operation andi in the normal at-Y IB of relay CY until operation to` tran's'nnty transmits either controls or indications during an operating cycle; and the nature of each operating cycle is determined by the character oi the code element sent from the control oflice during the initial energization of the line circuit, conveniently termed the conditioning period.

Since the operation of the system for a control cycle and an indication cycle is somewhat different, typical operating cycles for transmission of controls and for transmission of indications Will be described separately.

Typical operating cycle for controls Before considering in detail the operation of the relays and the circuits involved for a typical operating cycle for transmission of controls from the control oi'lce to one selected eld station, it will be helpful to survey briefly the general functions performed during such a cycle.

When a particular field station, and the par- ,d ticular controls to be transmitted to that field at each of the field stations to identify the operating cycle as a control cycle.

Following this conditioning period, and when the line circuit is deenergized in the control office, the rst step relay VI is picked up in the control oiiice and at all the eld stations. The line circuit is then energized at the control oice with thefrequency fI or f2, as the case may be, in accordance with the character of the rst code element of the code call belonging to the field station to which controls are to be transmitted; and such energization of the line circuit acts to drop out the station selecting relay such as ISO at all of the field stations whose code calls do not match. This same operation is repeated for as many station selecting steps as required by the number of stations involved, only two such steps being shown, after which a station selecting relay such as ISO remains energized at only the particular station identified in the control office as the one to receive controls during this particular operating cycle.

After one field station has thusbeen selected, each energization of the line circuit with the frequency fI or f2 during subsequent steps is in accordance with the controls to be transmitted and causes operation of control devices, such as the magstick relay IWZ in Fig. 2B, to conform with these controls, thereby governing the operation of the switches and signals at this field station in the manner desired .by the operator.

After the control office has' intermittently energized and deenergized the line circuit for the prescribed number of step intervals, depending upon the number of stations and controls, the energization of the last step relay VL energizes a clear-out relay CO at the control oce, which applies both frequencies fl and f2 to the line circuit simultaneously for a clear-out control,`

which deenergizes the cycle marking relays CY and other relays at the controlofiice, and all field y stations, to restore the system tothe normal condition, ready for another operating cycle.

; the respective stations.

112 With this general explanation, consideration may now be given to the detail cir-cuits and relay operations involved in preparing th-ese functions. M anual start-Since controls in accordance with the positions of switch and signal levers or the like can be transmitted to only onestation at a time, and since it is desirable that the operator be able to manipulate these levers at any time he wishes, it is desirable to provide suitable means for causing the system to act automatically to send out controls to eld stations one at a time in some predetermined orderregardless of when the operator may happen to manipulate the control levers and actuate start buttons relating to This is accomplished in the organization shown by a group of manually operable start push buttons such as IPB, one for each eld station, with an associated repeater relay such as IPBR, and a code determining relay such as ICD, together with a master relay CDS and interconnecting circuits,

in the manner shown and described, for example, in the prior patent to Halles et al., No. 2,259,561, October 2l, 1941. f

As a typical example of such operation, assume 4. that the operator, after having positioned the r5,5; for relay IPBR shown, of certain other push i control levers belonging to the typical field station shown, pushes the start button IPB for this station. Referring to Fig. 4A illustrating the result- -ing sequence of relay operation, the actuation of button IPB energizes the associated repeater relay IPBR by a circuit readily traced on the drawing (see Fig. 1B) through a contact 24 of the push button IPB and a cancel button CNB, which is preferably provided to enable the operator to stop transmission of controls set up prematurely or by mistake. The relay IPBR sticks through its front contact 25 and a back contact 26 of its associated code determining relay ICD.

Assuming that no other code determining relay such as ICD for any other station is energized at this time, the energization of relay IPBR establishes a pick-up circuit through the upper winding of the associated relay ICD which may be traced from (-l-), through the back contact 21 of relay CY in Fig. 1A wire 28, back contact 29 of relay CDS in Fig. 1B, front contact 3l! of relay IPBR, upper winding of relay ICD, and cancel button CNB, to

In this connection, whilev only one relay ICD is `illustrated, it should be understood that there are a number of such relays, one for each iield station, and that the pick-up circuit for each oi these relays includes a back contact, such as 30 button repeater relays belonging to other iield stations, in such a way that these relays such as ICD are energized only one at a time in a prescribed order determined by their electrical oonnections. `The relay ICD for the one station l"shown is assumed to have preference over all others, since their pick-upcircuits (not shownbut partially indicated at 3i) are broken at the back contact 30 of the associated relay IPBR.

The energization of the code determining relay vICD opens its back contact 25 to release the relay IPBR, but at the same time a iront contact 32 of relay ICD establishes a stick circuit through its lower winding `in series with the master relay CDS which may be traced from (-l-), through 'back contact 34 of relay C in Fig. 1A, in multiple with a back contact 35 of relay CO, also in multiple with a back contact 36 of relay CY, wire 31, winding of relay CDS in Fig. 1B, front contact 32 of relay ICD, its-lower winding, and through,

contact 38 of relay CDS in Fig. 1B, Wire' 3,9; re.-

lay C, back contact lill of relay FC, to-

It may be noted here that the back contact IIIIv ofI relay FC is included in this energizing circuit for the control cycle relay C, in order-toprovide the necessary interlock in case a i'leld start pulse is received before or at about the same time the operator manually actuatcs a start button IPB. If the eld start pulse is received in the control oflice to energize relay FC, in a manner later explained,

before relay C is energized by the manualstart, then the-manual start is vnot effective for that particular cycle.

The master relay CDS. when once energized, is maintained energized until the end of the current operating cycle, and the control` cyclerelay C is likewise maintained energized to the endy 0f this cycle.

Conditioning period ,for d. control. cycle- Still referring tothe sequence diagram of Fig. 4A, thev energization of the control cycle relay C of Fig. 1A4 in the control ollce establishes a circuit fOr en-y ergizing the relay P2111 the control oceto render the oscillator for frequency f2 active. to applythis frequency to the line circuftthe. energizing circuitv for the transmit relay P2 under these conditions being traced from through the backcontact.. t2 of relay E in Fig. 1A, through frontcontact 43' of relay C, wire lill, through back contacts 45 to 119 in series of the stepping relays VL-VI, and a connection 5t from the back contactof step relay VI to f2 bus, and through the Winding of relay P2 in Fig. 1A, to

This energization of the transmit relay P2, for applying the frequency f2 to the line circuit, closes an energized circuit for the line repeater relay FP in the controloilice from through a back contact 5I of relay Pl; and a front contact 52 of relay PE through the Winding of relay'FP, to This energization of the relay FP closesv a pick-up circuit for the cycle marking relay CY, from front contact 555 of relay FP,.relay CY' to and relay CY is then stuck up by a stick circuit including its front contact 54' and back contacts 55 and 553 in multiple of the relays PI and P2.

The energlzation of the cycle marking relay CY in Fig. lA in the control cinco and closure of its front contact ifi establishes a circuit through front contact l? of relay to pick up the relay VP in Fig. 1B, Wl'l of the relay E in Fi` lA to open its back Contact ft2 and interrupt the energizing circuit for the transmit relay P2 for frequency f2 previously described, thereby terminating the conditioning period.

During this conditioning period, all of theilelcl stations are c "ioned to receive a controlcycle; and a descr el'tl station own in Figs. 2A. andZB applies to all the. field stations. Referring, to Fig. 2A,. the transmission of the frequencyl f2 from. the control.-

ofce. energizes. receiving relay F2 which.. amongA in turn causes energization` :is operation for the typicall other-things, operates its contact linger 60 1:01`

close :a front contactwhle the contact linger. 6I ofl relay FI remains in its deenergized position,

and; establishes` a pick-up circuit for the relay ISC, which` may betraced from through back contact 62 of relay ICY, iront contact 63 of.

lished only momentarily, because both the backl Contact 6'2" of relay- ICY and iront contact 63 of relay I-Loperate shortly after the relay F2 picks up, as presently explained; but as soon as the relay l-Siis energized, it closes a front contact l2. to supply current to this circuit in multiple with. ther backl Contact S2 of relay ICY and front Contact 53 of relay IL, and thus rriaintainv relay IS@ `energized so long as relay F2 is energized.

Theenergization of the receiving relay F2, in

response to the` conditioningfrequency f2 for a control cycle, opens at its back Contact 'i3 a stick -'circuit throughn the lower Winding of relay IL from (-i-), through back contact 'I4 of relay-FI, back contact lf3 of relay F2, front contact 'I5 of relay lL, through its lower winding, to The relay LL is= preferably made slightly slow releasing, as indicated, so that there is time for energizationfoi the relay ISO over the pick-up circuit previously traced.

The energization of the receiving relay F2 also picks upthe line repeater relay IFP- by a circuit from (+L through back contact Tl of relay FI, fronti contactl l of'relayFZmvinding of relay FP, to-

The energizaticn` ofthe-linerepeater relay IFP in turn picks up; the cyclexmarking relay ICYby acircuiti from (-H, through front contact 'I of relay'iFP-front contact 'iSiofrelay I'L, and Winding oi relay iCY, to and the relay I CY is-r held, up by a sticht circuitI until the end ofthe ,Y current. cycle through itsv own front contact 8e,

and. backV contacts 8l' and 82"` in multiple of the receiving relays F7! andll Thexenergization. ofy the' relay ICY and closure of its irontcontact E2, Whilethe relay IFP is also energized*v to close its: front Contact 84, causes energization of the relay INP in Fig.,2B to conditioni theY stepping bank for operation, in the same meunierv asi in the control oice.

Typical station selecting step. Fig. 4B is the sequence diagram` for this operation. When the.

line'cirzcuit is deenergized. at` the control oiTc'e to terminatethe conditioning period, the repeater relay lll? -in the controlfoliceandsthe repeatervrelays such as; IFP-'at all the eld stations release, andy the rst steprelaty VIy is energized in theusu'al: way characteristic of the stepping banks shown, as described more inL detail in the prior patent. to Judge, No; 2,138,863, December 6, 1938.

In the controls office, this energization of the first step relay Vif establishes circuit connections to permitv energization of the transmit relay PI orPllk in accordancewith a first code elementof thecode call for the,` field station toA which the controlsin. question' are'. to be transmitted. As a typical example ot thisy operation, and` assuming the code determining. relay ICD shown isenergized, with code-connection. as-shown, the circuit for energizing; the transmit: relayl? I: upon thezienergizationA of. the -rst stepfrelay VI maybe-tracedfrom (-1-) tl'iroi-lsh1 baclccontact, 4-2wo relay E; in..

155` Fig. lA, front contact ll of relay C, wire 44, through back contacts l5-43 of step relays VL- VZ, front contact 49 of step relay VI, code bus 86, through front contact 61 of relay ICD, code connection 13S to the fi bus, through the transmit relay PI, to

The operation of the transmit relay PI, and the resultant energization of the relay FP in the control oiiice, releases relay VP in Fig. 1B, and with relay Vi energized, establishes a circuit to pick up the relay E in Fig. 1A to open its back contact 42 to terminate this energization of the line circuit with the frequency fI.

Considering now the operati-on occurring at the eld stations as a result of the energization of the line circuit with a particular frequency fl corresponding with the rst code element of the code call for the field station being selected, it is convenient to explain first how the station selecting relay ISO for the typical station shown is maintained energized under these conditions, due to the fact that it is the station being selected. When the receiving relay F2 releases at the end of the conditioning period, it opens at its front contact 613 the control stick circuit then energizing the relay SSO; but very quickly thereafter this same relay 'F2 establishes an auxiliary stick circuit to hold up the relay ISO during the subsequent ofi interval, this circuit being traced from through back contact 14 and 13 of relays Fi and F2, back Contact 15 of relay IL, front contact il@ of relay ISO, and back contact 'lil of relay ESI to In other words the control stick circuit for the relay ISO, which is dependent upon the energization of the receiving relay F2 in the case under consideration, is broken just before an auxiliary stick circuit for this relay ISO is made up through the back contact of the same relay F2; and While the contacts of the relay F2 may be adjusted to perform a make-before-break function, the relay ISO is preferably made slightly slow releasing by the use of a rectifier as shown, or by equivalent means, so as to hold its armature in the attracted position and maintain its front contacts closed during the brief interval required for the contact fingers of the receiving relay F2 to move between their front and back contacting positions, as diagrammatically indicated in the sequence diagram of Fig. 4B.

Upon energization of the line circuit with the frequency fi for station selection purposes, the energization of the receiving relay FI opens the stick circuit for relay ISO above mentioned through its front contact 98; but at substantially the same time the front contact 6I of the relay Fl closes to provide a control stick circuit for the relay ISO through a code jumper eiective with the step relay VI energized, this circuit being from (-l), through front contact 12 of relay ISO, back contact B0 of relay F2, front contact 6I of relay F, fl bus, back contacts 92-95 of step relays Vlr-V2, front contact 96 of step relay Vl, code jumper 91, stick bus 98, and front contact 90 of relay ISO through its winding and back contact 10 of relay SI, to

When the receiving relay FI releases upon termination of this on interval and breaks the control stick circuit through the code jumper 91 above mentioned, the auxiliary stick circuit for the relay ISO is established as soon as this relay FI closes its back contact 14; and as above noted, the relay ISO is made sufciently slow releasing to hold over this relatively short interval between 16 breaking a front contact and closing a back contact on the same relay FI.

Considering now the operation at field stations having code calls which do not match that being transmitted from the control office, it can be seen that, when the receiving relay FI at such stations opens at its back contact 1li the auxiliary stick circuit for its relay such as ISO, that relay at each of these stations at once releases, because the code jumpers at these stations do not provide the necessary contol stick circuit for such relay. The release of a station selecting relay such as ISO at any eld station in this manner opens its front contact 12 to prevent its energization on any subsequent step, where the code element transmitted in the way of frequency fl or f2 may happen to match the code jumper. Also, the release of the station selecting relay such as ISO at any station opens at its iront contact IUD the pick-up circuits for the stepping relays, so that further stepping operation stops at such rejected station.

The same operation of applying an impulse of the frequency fl or f2, in accordance with the code characters associated With the code determining relay such as ICD then energized, may be carried out for as many station selecting steps as desired, only tWo being shown; and the same operation of holding up or releasing station selecting relays such as ISO is repeated for the successive code elements of the station code call, until there is only one station selecting relay such as ISO left energized at the particular selected field station, the others having been released during some one of the previous station selecting steps, in a manner which can be readily appreciated without further explanation.

After the last on period for station selection (two being used in the particular simplified arrangement shown), the energization of the next step relay such as V3 during the next off period connects through its front contact IBI to the stick bus 98 to hold up the station selecting relay such as I'SO at the particular station selected.

Transmission of a typical control- After the station selecting steps, the transmission of frequency fl or f2 on the succeeding steps is determined by the position of the switch and signal levers or the like; and an explanation of the operation of transmitting one typical control, in accordance with the, position of the lever SWL shown, will serve to make clear how any desired number of -controls may be transmitted to a selected eld station.

Referring to Fig. 1B. and sequence diagram of Fig. 4C, the energization of the step relay V3 following the transmission of the last station selecting impulse in a simplified arangernent shown, renders the position of the lever SWL effective to determine whether transmit relay PI or P2 shall be energized. Assuming the lever SWL to be in the position shown, it can be seen that the fl bus is energized through the contacts of this lever, front contact HD2 of relay ICD, code bus |33, and front contact i1 of step relay V3. Thus, in the arrangement shown, an impulse oi the frequency JI is transmitted for a switch control.

Referring to the field station apparatus in Figs. 2A and 2B, the energization oi the receiving relay FI in response to the impulse of irequency fl, resulting from the energization of transmit relay PI, establishes a circuit through the upper windingof the mag-stick relay WZ of for the cycle marking lig. 2B`throughfronttcontact ISIIiof'StepreIayVS, this fcircnit being vfromz(l), through front' contact I2.of relay ISO, still energized at'thefzselected station in question, back contact $0 of relay/F2, front contact tl tacts 92, 93 ofstep relays VL andVd, frontconta-ct 94 vof step relay V3, upper Win'dinglofamag-stick relay WZ, returnbus M35 throughironticontact |06 of relay ISO, to

'hisv flow oi current through the upperzwindingr l0' of the. magsticli'y relay WZ positions .its contact ngers to a positionpcorresponding'Witlrithescontrol lever SWL in the control office; .andeffecting the desired control of. a switclrorother device connected thereto. A. magnetic stick typezrelay? WZ with two separate operating windings,- which acts to hold its contactfingers in thelastzoperated position until changed, has been' illustrated, in the interests of simplicity; but the samer'control circuits may be employed to govern :the energiza-f tion of separate neutral relays with decodingrrelaysand execution circuitsin the mannerrdis closed for example, in the patent to Wells, No. 2,559,922, May 23, 1939;.

It can be readily seen that a similarioperation4 may be repeated for another controluponenergiza-tion of the neXt step relayy Vgtandfior. as many other control steps as. desired.

Clear-out after 'a control cgfcZe.-From the foregoing explanation it-canibe seenthat thesteppingf; operationk is `performed -in this system inl response to intermittent energization anddeenergization of the line circuit .at the controloflice; ,andiwhen the stepping bank in the control oiice hasta-igen the prescribed number. of steps, depending uponr. the capacity of the system, andthe last stepping relay LV isV energized, a: quickclearoutior restoration to normal is .accomplished byenergizing the line circuits si.inultaneously with frequencies f I and. f2.

Considering this operation more -in detail; and referringy to sequence chart for they clears-out period in 42D, the energizationfothef last stepping relay LV in Fig. 1B atthecontrol fo-fi'ce closes a front Contact Imi-to apply tea wire: it), connecting to the clear-out relaylCO'lirr-Fig. 1A, thereby energizingv thisrelay CO'ltcclose its front contactsV i iii and' 35 and energize' both of the transmit relays-PI and P2 atthe'sametime. he opening of both 'the back `these `:relays Pi and Pi'opens'the stic`lfz'circuit relay CY;y and* since'. the relay FP is not energized' with both oftheffront contacts iii and 52 of these relays PIQand P2 cally released, opening its frontcontacts `IIzv-tnd I9A to restore the VP relay and steppingrelays Vi-V'L to their normal conditions.

The release of the last step rel-ay. VLopecns its front contact 198 to deenergize the relay .COLA and relays VL and CO` are preferably slightly slow acting in releasing as indicated,` Afor timingpurposes later discussed; The ultimate releaseofihe relay CO opens its contacts 34 and iIIltorelease the transmit relays Pi and P2', and terminate the conditioning period.

Referring to theapparatus at the ieldstations, the energization of both receivingrelaysFI and F2 at the same time drops the cycle..marking relay such as ECY at each' ield. station bfyopening at the baci; contacts 8i' and r52of.relfa'ysll and F2 the stick circuitfor the relay iCY,`,Wlifi 1e the relay iFP fails Ato pick up. This restores ythe l stepping relays lVL IVL1 ,and` half-'step"relay,v

ofrelay El,..flib.us,=.back con-f 5 the stick. circuit ythroughr thelower: WindingI of relay IL is established through"backecQntacts-,'

'Mfin series oir` these .-relays.l FI- andrFZ. and 'front contact -.'I5- of relayjIL.:

The. station selecting. relaygsuchy ias I SO. at lthe particular ieldstationselected forl the" control yclef in qeustionreleases whenfstepjrelay V3 drops; and opens .-itsffrontwcontact .I0iI,- the-stick circuit through its. .front contact l2.. being. open becausezboth V.front `contacts 69il of -relays-Fi :and F2'. are closed.-v amin itsf auXiliary-f stick' @Denit through its. otherv front Contact Si): being .broken at .the backvcontaots 13andflllofrelaysilil and F12l- In this: Way,l 4the apparatusatallwfield. stations is.` resto-red to. the normal..at.rest condition .at y.the end of acontrolcycle relatively quickly.by the operation of quick actingmelays, ras .distinctive fromthevclearfout .operation ordinarily employed andlinvolving aprolongedldeenergization of the line. circuit.. to releaseslow actingrelays... Also, since sl 0W.. release .,relaysare.. not .i employed. .for clearfout -purpo.ses,..the conditioning period'. may be .made shorter thanrequired'lf lthe .energizetion .of .such relays... It'an .be'readily appreciated that such shortening both the conditioning .and

the yclearrout periods for. anoperating. cycle in accordance With" .thisinyention .materially shortens'tlie duration .of tliecornplete cycle, ,and speeds upA the' Operation 4of 'the entire. communication system.

Emergency,clear-oatfProvision is made inthe system of "this invention' for automatically causing the" same clear-out operation' by, energiza- 45,. tion .of .the relayv CO, in .the event the line circuit closed; this cycle marking relay CY'isautornati-A should 'be cbrnesteadily .energized .or deenergized .durin'ggan ogeratingeycle; dire'. l.toen open code lbusor' soniefotlier fault.'V .Sincesuclifaul y 4condition Aof "the ,circuit's. may,y beof'a transitory-.nature and mayl disappear-I upon ylsorne sulolsequent operation, or. mayinvolve apparatus relating. to only one .o f he yseveral.stations, :itpis ,desirable in theinterests of 'racilityto provide an.. automatic clevar-out Iunder such.. conditions, rather than leave 'the system stalled 'until 'some special inanual manipulation or repairJis made` ReferringLto Fig.. 1A, tyvo.. s1ow'. releaserelays rSX and OCare gpyerned'by Vtheli'ne repeater relay andimpulsingirelayEQso thattlie relay .0101s released 'ifrrrereiis fapsustainedenereizanon .oftheline circuit, and the. relay SX'andLin turn relay O'C'are released if 'the lieccirczuitlldecomes deenergized ,duringan operating cycle for a.pro longedpveriodf The releaseofftlverelayQC. in either' case. yand closure -of its vfb'acli contact. .I @I 3 ,establisheseJ -circuit, readily.tracedthrougliiitont ,contact jt "of relayCYxandwvvire ,I L4 for .energizing the clear-.out .relay .,CO,y .which zacts. to .restore the .apparatus in .thecontrot .office .and at each ,.eld station .to the.. `norma-1 condition. in kthe. regular .Way-

Considering .thefcontrol .of .theselyrelaysSX .and QC .more -in .d-taiL. under. 5th-e normal- .condition shoWn,the.relay,iSX,is maintained energizedloy. a through i beckacfmteet. :l vf

' relay CY, and the relay OC is maintained energized by a circuit through a back contact IIS of relay FP, and a front contact IIS of relay SX. When the relay CY is energized at the beginning of an operating cycle, the relay SX starts to time, and if the line repeater relay FP is not energized during the conditioning period, or at frequent intervals thereafter during the operating cycle, to close its front contact I I and re-energize the relay timing of the relay OC, which in turn will cause the automatic clear-out.

Thus, if during an operating cycle the cancel button CNB should be operated, or a broken wire or defective contact should prevent the energization of a code bus to pick up the transmit relay PI or P2, the resultant failure to energize the line circuit causes the relays SX and OC to release in turn and cause an automatic clear-out operation.

If, however, there should be some broken wire or bad contact in connection with the stepping relays to prevent energization of the impulse relay E to cause de-energization of the line circuit during an operating cycle, the energizing circuit for the relay OC is open at the back contact IIS of relay FP and front contact 42 of relay E, so that this relay OC times out and produces the automatic clear-out control.

Thus, if there should be a sustained energization or deenergization of the line circuit during an operating cycle, on account of certain circuit faults, an automatic clear-out operation is effected to restore the system to the normal condition, ready to carry out a subsequent operating cycle, if such may be done under the existing faulty conditions. t

Stored 'manual starts- As previously noted, the slow release characteristics of the last stepping relay VL and the clear-out relay CO are employed during the clear-out period for timing purposes, and in order that any manual field start in the control cnice then existing and stored may be at once effective to assure a succeeding control cycle without delay.

Considering this feature more in detail, and referring to the apparatus in the control office and the sequence chart for the clear-out period in Fig. 4D, the energization of the clear-out relay CO and opening of its back contact 35 in Fig. 1A breaks the stick circuit over wire 31 to the code determining relay, such as ICD, then energized, because the back contacts 36 and 34 of the relays CY and C in this stick circuit are open at this time. The master relay CDS in series in this stick circuit is also released, and in turn releases the control cycle relay C to close itsback contact 34 and prepare a stick circuit for another code relay such as ICD, which may thereafter be picked up due to the energization of its associated push button repeater relay such as IPBR, when the cycle marking relay CY later releases and closes its back contact 2.

Thus, if a manual start has been set up in the control ofce by the energization of a push button repeater relay vsuch as IPBR, at the end of an operating cycle then in effect, the code determining relay such as ICD for the corresponding station, the master relay CDS, and the control cycle relay C are immediately energized during the clear-out period to call for a control cycle. In such a case, when the clear-out relay CO releases,

vthe transmitter relay P2 is held energized over the circuit previously described for initiating a conditioning period for a control cycle; and consequently, this conditioning period occurs immedi- SX, it opens its front contact I I6, and starts ately after I to change the energization '20 the other transmitter relay f1! releases of the line circuit from both frequencies f2 and fl to the frequency f2 alone.

In other words, where a manual start exists in the control office at the end of an operating cycle, a control cycle immediately follows without any deenergization period, the energization of the line circuit with the frequency f2 alone acting to condition the system for transmission of controls the same as if this frequency f2 were applied after a period of line circuit deenergization.

This feature of permitting the control oilce to set up conditions for a control cycle during the clear-out period of an existing cycle either of controls or indications not only avoids a time interval between succeeding cycles, but also gives definite preference to a control cycle and obviates any race or conflict between a manual start in the control office and a field start from some field station, it being impossible for any field station to send such a field start pulse until the line circuit is wholly deenergized and both receiving relays FI and F2 are deenergized, as will be presently explained.

The foregoing explanation will serve, it is be-1 lieved, to make clear how the system of this invention operates to select a particular field station and send controls to that eld station in accordance with manual manipulation of control levers and start buttons by the operator in the control office, and also provide an automatic emergency clear-out and the desired preference to control cycles.

Operation for a typical indication cycle The operation of the system during an indication cycle for transmitting indications from a given field station to the control ofiice involves operation of the stepping relays and the like in substantially the same way as during the control cycle; but there are differences in the operation of designating and registering the particular station to send in indications, and other features of the operation which require separate consideration.

In general, an indication cycle is started out with a conditioning period the same as a control cycle, but with the other frequency fl. Following such conditioning period, the line circuit is intermittently energized and deenergized to operate the stepping half-step relay VP and step relays VI-VL, and the relay E in the control office the same as during a control cycle; but the frequency character of the successive energizations the line circuit is controlled in a different manner for station selection purposes, and in connection With continuing the stepping operation for transmission of indications.

Briefly outlining the functions for an indication cycle, a change in the position or condition of any device at any eld station calling for the transmission of a new indication to the control oice, such as the energization or deenergization of a track relay by train movement out of or into a track section, causes such field station to apply a short starting pulse of frequency f3 to the line circuit, which acts in the control office to energize a field control relay FC to initiate operation of the system for an indication cycle.

Since indications can be received in this type l of system from only one field station at a time Whic antenas one istation .at a time, some isuitableximeans. must be provided to exercise a perference or'priority as between such plurality of -eldstationssattempting to transmit indications Iat thesame time, in such a way that thesestationsare rendered effective only one at a ,time to transmitiindications during successive operatingcycles.

In the system of this invention,I this preference or priority for eld station transmission is accomplished in accordance' with the general principles of code superiority discolsed in our prior patent No. 2,129,133, SeptemberfG, 1938. In a carrier current type system, however,l a eld station with a superior code'call may not beable to effectively exercise its code superiority directly against other field stations .by controlling thexline circuit condition, as inourzpriorfpatent, because the existence of a nodal `line circuitzdeenergization due to the eifect of standing'waves, in acarrier current system, or the phase oppositionnof frequencies at a given station as Ireceivedfrom different oscillators at other field stations, may preclude response of some .station or stations to an energization of the line circuit created `at some otherstation. For these reasons, the principles of code superiority of our prior patent above mentioned are applied differently in the system of this invention by whatmay be termed'in-andout transmission to and from the control office of the superior code elements calledfor by thewfieldi stations trying to send indications at thesame time.

Briefly considering this planofoperation, later described in detail, each field station having new indications to transmit is `given opportunity, until dropped out, to send a code element .to the 'control oflce during cach off interval inthe station selecting portion of the cycle, namely, 4the first two steps in the simplified arrangementzshown. The application of a pulseoffrequency f3, as distinc tive from a non-pulse condition, constitutes the superior code element; and eld stations may send in their indications during. successive indication cycles in the order determined .by the relative superiority of the station codecallsallotted to them, the superior field station being the one having a code call requiring the greatest number of requency pulses occurring earliest'in the code. For example, in the case oftwo station selecting steps as shown, and using p to represent a pulse of carrier frequency f3, and O to represent the non-pulse condition, the order or preference for the four stations is (l) p-p; (2) p-O; (3) O-p, and (fi) O O.

During each of the field station selection or rejection steps, if any one of the .plurality of stations in action sends a pulse of frequency f3 tothe control office, the reception of this pulse of the field frequency f3 in the control oiiice causes thecontrol oflice to respond by transmitting the frequency fi, which is arbitrarily taken as a code element superior to the frequency f2. The reception of this impulse of the superior frequency fi from the control oiiice, at each of the plurality of field stations then attempting to ysend in indications, holds up an indication station selecting. relay such as iSI at the stationy or stations having a corresponding superior code element in .their code call, but automatica-ily drops out such relay HSI at each field station or stations vhaving acorresponding inferior code element,

If. however, no pulse voi? field frequency rf3 is received at the control oiiice from any station, it with the other inferior. frequency f2, h maintainsV energized .the indication select- 22 =ingirelay;i.suchiasirelayaISLc at; any station or stationssti-ll havingrthisrrelay energized.

This .same operation of ,holding or rejecting field istations in :accordance with .the relative superiorityrof their'. code calls may be continued fori asairrianyustepsi:ais-desired, ydepending upon theinurnbernofstations; and at the end of this stationireiection period, one station selecting relay', suchzasrelay ISI, is maintained energized at onlyionezisending station; which. is tnenieftectiveito createy pulses or non-pulsed conditions of Ithe lineacircuitwith the frequency f3 during the subsequenttsteps.C for operation of the indicating devices :iin-fthe Icontrol ofce.

Alsopduringthisstation selecting or rejection period, certain station registration relays in the control. office are operated in accordance with the station code call retransmitted from the control Lolitec, so that the indications subsequently yreceivedfrom the surviving station are directed -toftlief particular indication storing devices belonging \to that station.

Theficleareout period at the end of an indication-'.cycie occurs the same as for a control cycle,

f 25 exceptithat relays'FC 'in the control oflice and a relay'fsuchias ISI is released at the surviving field station, rather thanthe relays Cand ISO previ'ously. described which relate to the transmissionzofzfcontrols;

It may be pointed out-here that, since the relay,'fsuch' as-relay"ISI, fortransmission of indications.iscontrolled'in th'e same Way as the relay, such asfrjelay` ESO, b'yvimpulses `offrequency fl or f5. 'transmitted from the control ofiice, it is '35 convenient "to fuseith'e same code call for identifyinggtheiield'sta'tions for controls and indications, andernpl'oyfin the same circuits vand code jumper connections: fori governing both relays ISI and ISG.

Withthfis general explanation of vthefunctions for an indication cycle, considerationmay lbe given `.tor-the detail circuits and relay operations `involved-Vin Iper-forming their function-s.

Field-'startL-'Referring toFig. 2B and sequence ldraagrarnfof fFig. EE, wheneverl a lchange occurs in the device fatwa' leld station cal-ling for the trans- -missionoofnew' indications, such as they energization or deenergizationof the track' relay ITR, a stickicircuit-for a changerelay iCH through `its frontfcontactizt is momentarily broken during the ymovementof the contact finger IZ-I of the Itrack` relay II'IiPt from one position to thev other, south-'at the'fast operating change Vrelay lICH is de'energized. The-closing of a back contact vI22 ofy relay ICI-I establisliesan energizing circuit forca repeater relay'ICHP, which may be traced from through 'a back-contact 23 of relay ISI, wire |211, also connected to (-i) `through a back contactl IiZtiof relay IVL, relay `ICI-IP and back contact `I 22 'of relay ICH to This energization*of'relay ICHP closes a front contact i126' to provide a stick circuit for itself independently ofthe `relay ICI-I, and also closes a front contact 127' to providea lpiclnup circuit 'for relay ICHthrougha back contact i223` of .the step relay, V3i representing. the rst indication step-- ffor reasons ziater explained..

Assuming.` the system to be in. the normal 7U at-rest position as shown, the energization of the relays-I CHR in this.y way;4 provides a circuit yfor energizing, :the `pulsing relayi IPL which may vloe traced from ,(fl-, ,through back contacts'M and .13.iniseriesof thereceivingrelays FI and F2 `in 23 vWirev Ii, front contact |32 of rel-ayI ICI-IP to pulsing bus |33 through relay IPL to This energization of the relay IPL applies a short pulse oi the carrier frequency f3 to the line circuit as a field start pulse, the oscillator at position shown to the right-hand dotted line.

position, Assuming that no manual field start has occurred in the meantime to energize relay C, this movement oi the lower contact finger ISS oi relay M. establishes a pick-up circuit for the ield control relay FC which may be traced from..

from B, through back contact |31 of relay CY, lower winding of relay FC, through back contact |38 oi relay C to B, a suitable resistance being employed if necessary to regulate the intensity ci current through the winding of relay FC. The relay FC is then maintained energized by a stick circuit from (-1-) B, through .back contact |39 of relay CO, iront contact Ili oi relay FC and its upper winding, and back contact |38 of relay C to B.

Conditioning for indication cycles-Thus, in response to a field start pulse, the relay FC for an indication cycle is energized and the upper contact linger |35 of the relay M is operated to the righthand position. Under these conditions, a circuit is established to energize the transmit relay PI from through back contact 42 of relay E, back contact 43 of relay C, front contact |42 of relay FC, now energized, contact finger |35 of relay lVi to the right, and connection |43 to the fl bus relay PI to This energization oi the transmit relay PI in the control oflice energizes the relays FP, CY, VP and E the same as during the conditioning period for a control cycle, as indicated in Fig. 4E'. Also, at each field station the energization of the receiving relay FI operates relays IFP, ICY, IL and IVP the same as for a control cycle.

The energization of the receiving relay FI at the field stations, however, does not energize the station selecting relays such as ISO, which require energization of the relay F2, but at each iield station having its change repeater relay such as ICI-IP energized, a circuit is established for picking up the relay such as ISI at these eld stations, this circuit being similar to that previously described for energization of the relay ISO, but including a front contact 6I of relay FI, ,fI bus, back contacts 92--96 of stepping relays Vlr-VI, front contact |44 of relay ICHP, wire |45, relay ISI, and back contact |46 of relay ISO to The relay such as ESI at each field station for transmission of indications is provided with control and auxiliary stick circuits operating in the same way as those for the station selecting relay like ISO, so that such relay ISI remains energized at any field station only so long as the station selecting impulses of frequency fI or f2 correspond with the code jumper connections and code call of that station,

The energization of the receiving relay FI opens at its back Contact lll, and the release i the relay iL later opens at its front contact |30 the circuit for energizing the pulsing relay IPL upon A energization of the associated relay ICHP. Conback contact M6 of relay ISO to circuit is closed very quickly after the energizing sequently, as lsoon as the conditioning period for an indication cycle is started, any subsequent energization of a change repeater relay such as iCiiP at any station other than the station or stations ready to send indi-cations at the time of such conditioning period, is not eiiective to energize the associated pulsing relay such as lPL, and create premature or false pulses of the field carrier frequency f3 during the ensuing cycle. In this connection, it can be seen that the change repeater relay such as ICI-IP may be energized at any station during an operating cycle, whenever a change occurs calling for the transmission of new indications, so that a field start condition is stored ready to render the corresponding field station effective to send in indications on some subsequent operating cycle. y

Station registration. ln practical operation, often only one field station may have new indications to send to the control ofce at the time an indication cycle is initiated; and before considering the more complicated situation where it is necessary to exercise a preference or priority as between a plurality of eld stations trying to send indications at the same time, it is convenient to explain rst the operation oi station registration and transmission of a typical indication where only one field station is involved.

Starting with the conditioning period for an indication cycle, and assuming the typical field station shown in Figs. 2A and 2B is the one t0 be registered in the control office and transmit indications, when the relays ICHP, ISI and IVP are energized during the conditioning period, a circuit is prepared for the energization of the eld pulse relay IPL during the next succeeding ofi period, if the code call allotted to this eld calls for such a pulse of the eld frequency f3, as in the case of the typical field station shown.

Referring to Fig. 2A and sequence diagram Fig. 4F, when the receiving relay FI releases at the end of the conditioning period, an energizing circuit prepared ior .the field pulse relay IPL is established, which may be traced from through back contacts lil, 'i3 of relays FIy and F2, front contact i5@ of relay ESI, wire I5I, front contact |52 of relay lVP (see Fig. 2B) now closed, through the back contacts |53-l55 of relay IVL, IVl and IV2, code jumper or connection |56 to the pulsing bus |33, winding oi relay IPL to This energization of the relay IPL and the closure of its front contact l acts to render the oscillator OSC-f3 effective to apply the field frequen-cy to the line circuit; and at the same time the back contact il of relay IPL releases its repeater relay IPLP to open its contact 8 and terminate this pulse. When the rel-ay IPL is energized, its back contact It opens up the connecting circuits to the filters for frequencies fI and f2, but when the repeater relay IPL drops,

rthese filter circuits are again closed through the back contact l5of this relay, ready to receive frequency impulses from the control cnice.

When the receiving relay Fl drops at the beginning of the rst off period under consideration, it closes at its back Contact 'it a stick circuit for the relay IST., similar to that heretofore described for the relay ISO, and which may be traced from through back contacts 'i5 and i3 of relays FI and F2, back contact 'i5 of relay iL, front contact |58 of relay ISI, winding of this relay, through This stick circuit through front contact tI of relay FI opens the circuit then maintaining relay ISI energized; 

